The present invention generally pertains to tunable narrowband spectrometers and is particularly directed to an improvement in such spectrometers as include an acousto-optical tunable filter (AOTF).
Spectrometers are useful for detecting the concentration of given substances in a spatial region of interest, and are commonly used in systems for a myriad of such applications, including monitoring the levels of pollutants in automobile and industrial plant emissions and detecting the presence of toxic gases in a region of interest.
The use of an acousto-optical tunable filter in a tunable narrowband spectrometer is described in an article entitled "Fiber-Coupled Acousto-Optical-Filter Spectrometer", NASA Tech Briefs, May 1993, pp.42-43. The narrowband spectrometer described therein includes a discrete broadband visible or infrared light source; a first optical system disposed in relation to the light source for collimating light from the light source, for transmitting the collimated light through an acousto-optical tunable filter and for focusing the filtered transmitted light to the input of a first optical fiber; a second optical system for collimating light from the output of the first optical fiber, for transmitting the collimated light within an optical path through a region of interest enclosed within a sample cell and for focusing the transmitted light to the input of a second optical fiber on the opposite side of the region of interest from the first optical fiber. The filter is tuned through a predetermined series of different wavelengths that are characteristic of an energy absorption spectrum for one or more given substances; and a detector is coupled to the output of the second optical fiber for detecting the energy of the filtered transmitted light at each of the different tuned wavelengths to thereby provide a signal indicative of an energy absorption spectrum for the region of interest at wavelengths that are characteristic of the energy absorption spectrum for the one or more given substances.